Bump gridstack from 11.5.1 to 12.1.1 in /freedata_gui

Bumps [gridstack](https://github.com/gridstack/gridstack.js) from 11.5.1 to 12.1.1.
- [Release notes](https://github.com/gridstack/gridstack.js/releases)
- [Changelog](https://github.com/gridstack/gridstack.js/blob/master/doc/CHANGES.md)
- [Commits](https://github.com/gridstack/gridstack.js/commits/v12.1.1)

---
updated-dependencies:
- dependency-name: gridstack
  dependency-version: 12.1.1
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

freedata_gui/package.json

@@ -35,7 +35,7 @@
     "d3": "^7.9.0",
     "dompurify": "^3.1.6",
     "gettext-parser": "^8.0.0",
-    "gridstack": "^11.0.1",
+    "gridstack": "^12.1.1",
     "i18next": "^24.2.2",
     "i18next-vue": "^5.2.0",
     "js-image-compressor": "^2.0.0",